Compact power control
On the basis of a powerful switching field-effect transistor, for example, IRLR2905, you can gather compact controller capacity heating (soldering iron, heater) or lighting (incandescent wearable or stationary lights powered car the battery).
Diagram of a possible variant of such a device is depicted in Fig. 1. Its working principle is based on changing the on time of the FET.
On the elements DD1.1, DD1.2 is assembled, the generator of rectangular pulses. The frequency of their journey - about 15 kHz, the duty cycle can be adjusted in the range between 1.01 and 100 variable resistor R2. The elements DD1.3, DD1.4 is used as a buffer amplifier, the output of which control pulses arrive at the gate field-effect transistor VT1. At high (1.5...2) the logic level on the outputs of these elements, the channel resistance of the transistor is reduced to of 0.027 Ohms. At this point, through the load current flows, the value of which depends on its resistance and voltage. When the outputs of the elements set to low logic level, the transistor is closed and the current through the load does not flow. By changing the ratio between the residence time of the transistor in the closed state and the time when it is open, it is possible to regulate the average current through the load.
The regulator includes in series with the load, observing polarity. When indicated on the diagram the values and types of the elements of the supply voltage can be in the range from 4 to 14 V. Include its supply voltage on the chip DD1 through the switch SA1, combined with the controller is a variable resistor R2. When this during a time when the field effect transistor is closed through the diode VD4 and the switch contacts are charging the capacitor C1. When the transistor is open, the chip is powered by the energy stored by the capacitor C1. Since the current, consumed by the chip is small, the voltage across the capacitor is approximately equal to supply voltage.
The Zener diode limits voltage VD1 power the chip. The fact that technical specifications it should not exceed 15 In, but when the transistor closes in the wires connecting the device to the load, the EMF occurs inductance and the voltage across the capacitor C1 may exceed this value. When long connecting wires this EMF can be substantial, so in series with the switch SA1 is necessary to include a resistor R4 resistance some of the shortfall. By the way, this resistor is necessary and if the voltage power more than 15 V.
The controller can be applied microcircuits CLA, LA, LA, diodes series KD521, KD522. Resistor R2 - SDR-Rpm (with switch), the rest of the IFL, C2-33, P1-4, the capacitor C1 - K53-1, K53-1A, K53-18 or smaller for surface mount, C2 - K10-17-1.
The regulator collect on the PCB of bilateral foil fiberglass, a sketch of which is shown in Fig. 2,and. Details are placed on both sides (Fig. 2,b), traces the different parties connect wire lintels over openings.
The wires connecting the regulator to the load and the power source must be maybe shorter, with a length of more than several centimeters to reduce their the inductance must be recoiling.
The establishment of the regulator is reduced to the selection of resistors R1 and R4. It include in series with the load and in parallel with the contacts of the switch (they must be open, which between them put a strip of heavy paper) connect the milliammeter. Adjusting the load power variable resistor R2, control the voltage on the capacitor C1, which should be about 0.5 V less than the supply voltage. When the maximum load power it will decrease, R1 should be replaced by a resistor of greater resistance, and if, on the contrary, will be more of the supply voltage and the voltage reaches the Zener voltage VD1, you may have to install a resistor R4 (in this case from the printed guide, to which is soldered the output of the cathode of the diode VD4, remove the area bounded in Fig. 2,dashed lines).
Finally the need for the inclusion of the resistor R4 is determined by measuring the current, consumed by the regulator over the whole range of supply voltage. If he doesn't more than a few milliamps, the resistor R4 can be omitted. Otherwise if it is necessary to choose so that this current does not exceed 10 mA. When the voltage IPIT more than 15 In the resistor (in ohms) should to be not less than (u pit - 15)/0,01.
When the load current is more than 5 And the transistor solder (soft solder) to be mounted on a heat sink - copper plate with thickness of 0.5... 1 mm and an area of a few square centimeters.
Author: I. Nechaev, Kursk